Sales rose 3.6% in December compared with growth of almost 12% for 2018 as a whole, according to online retail body IMRG – which does not include Amazon in its figures. IMRG said low consumer confidence had put a dampener on spending.

The poor December topped off a difficult second half for online retailers, echoing their high street counterparts, in what IMRG called a “lopsided year”. Growth around the Black Friday discount day in late November slowed and Andy Mulcahy, strategy and insight director at IMRG, said those sales had not been picked up in December.

The numbers, which include data from more than 200 major retailers, indicate that even online-only players – which have benefited from the shift away from the high street – suffered in the last quarter of the year.

Mulcahy said: “The first half of 2018 was actually very strong for online retailers – it resisted and arguably benefitted from the tough climate that impacted trade for store retail. It is only the second half of the year where the suppressed confidence and spend, evident in so many other sectors, has spread to online retail; the macro-economic situation must be exerting pressure here, particularly with Brexit now entering its crunch period in the first quarter of 2019.”

Amazon, which is estimated to account for about 15% of total UK online sales according to analysts at retail consultancy GlobalData, has not revealed details of its trading in the UK over Christmas so it remains unclear if IMRG’s members have lost out to the online giant or whether the whole market suffered.

Patrick O’Brien, an analyst at GlobalData, said: “I think Amazon will have been posting very strong growth.”

But he said it was not surprising online sales of electrical goods were no longer rapidly increasing. “It’s a market that is already saturated with more than half of the market online. It is no longer a rapid growth market and online sales are decelerating to be more in line with total sales growth.”

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Bhavesh Unadkat at Capgemini added that online retailers were facing increased competition from cheap high street players, such as Primark, Poundland, Aldi and Lidl, that don’t sell online.

“Consumers were tightening the purse strings by taking advantage of promotions rather than purchasing more. This allowed discounters to take the share in the final month of the year,” Unadkat said.

IMRG predicts online sales will rise 9% this year, the lowest rate of growth recorded since it began monitoring the industry in 2000.

Mulcahy said retailers had become stuck in a cycle of discounting and faced challenges from uncertainty about Brexit and low consumer confidence.

“If Brexit can be resolved so that a course, whatever that may be, is agreed and pursued, it may help to build shopper confidence again with online likely to be the main beneficiary from a retail perspective,” he said.